This might lower risk for the customers because driver may take less risk without a helmet in some situation but the risk for driver is only increased.
This is optimizing for customers at the cost of drivers.
I don't see any supportive extensive research linked from them .
Also, the idea is to offer an option. Not to make it mandatory unless legislation require it. If your passengers are more comfortable not wearing them, their choice.
I suppose it's also not reasonable to provide seatbelts to passengers as well as the driver of a taxi?
No. Which means it's not automatically "the reasonable thing", just an opinion.
So I'm curious what the REASONING is behind your feeling that offering passengers the option to wear a helmet is unreasonable. Personally, I would AGREE that offering passengers on a pedicab the option of a pineapple would be unreasonable. There just isn't any practical correlation between pineapples and pedicabs. But helmets are different: there are large numbers of people who campaign vigorously to persuade others to wear helmets when on a bike; many places even have laws mandating helmets on bikes, at least for some ages. So it is a plausible thing for passengers to want. Given that, why would it be unreasonable to offer it?
I'd worry about lice.